LPD is available as liquid concentrate. Other than being more concentrated (dilute 1+4 for normal tone instead of 1+2) it seems to me exactly the same as that mixed from powder. It's more expensive, but if it's worth it to you, it's worth it to you. It's obvious, though, why the shelf life is bad. You can (with effort, it's tough plastic) squeeze the air out of the bottle and cap, but it will be un-squeezed again by the next day. Once you remove the foil seal from the top, it doesn't seal back even remotely air tight. I suspect (but haven't tried as I went to the powder) that just pouring the concentrate into your own bottles that you can cap air tight would make it last as long as that mixed from powder, maybe longer since it's more concentrated.

The only thing I don't like about LDP powder is that it dissolves reluctantly. I always seem to have a few grains of powder that just won't dissolve no matter how warm or how much I stir and I end up filtering them.